1. Field of the Invention
The invention relates to luminescent illumination systems for television, video and film sets and studios.
2. Description of the Prior Art
In U.S. Pat. Nos. 5,012,396 and 5,235,497 the Applicant, Paul D. Costa describes luminescent lighting fixtures and illumination systems providing omni-directional sustained luminescent (florescent and phosphorescent) light emission of desired color/chromaticity from phosphors in an emulsion coating the interiors of luminescent light tubes for television and film studios.
It is important to understand that there are both prompt or fluorescent and delayed or phosphorescent luminescent light emissions excited from the phosphors lining the light tubes. The prompt or fluorescent light emission begins within 10 nsec (10.sup.-9 sec.) of the exciting stimulus and ceases within 10 nsec after excitation stops. The delayed or phosphorescent light emissions can begin after 10 nsec of the exciting stimulus but persists beyond 10 nsec once excitation stops [See Van Nostrand's Scientific Encyclopedia6.sup.Th. Ed. 1983 pp. 1237, 1788 & 2204.] The bandwidths of prompt or fluorescent light emissions in many instances are different than the bandwidths of the delayed or phosphorescent light emissions. Also, the phosphor compounds which fluoresce may be different from those that phosphoresce.
As noted in U.S. Pat. No. 5,235,497, luminescent lighting fixtures have relatively large light apertures that generally frustrate efforts to direct and shape the emitted light. Even with the geometry for shaping the light from sustained luminescent lighting fixtures as disclosed in U.S. Pat. No. 5,235,497, the apertures can be unacceptably large, particularly when appropriate variations of shadows, and areas of differing luminosity, brightness, shade, tint and hue are required for providing a believable perception of dimensional depth to a two dimensional (flat) video or film image.
Color television cameras, video cameras, color photography films, digital electron scanning cameras and the human eye each sense or perceive discrete bandwidths of light which are then recombined, integrated and interpreted in a nonlinear fashion as a particular color. In contrast to incandescent lighting fixtures that are characterized with reference to Stefan-Boltzman "blackbody emission temperatures" or `color temperatures`, luminescence light consists of relatively narrow bandwidths of light emissions which do not follow blackbody laws. (A laser is a common example of a luminescent light source producing a coherent amplified light emission in very narrow bandwidths.)
Spectral output of luminescent light sources are better characterized in terms of an index which provides a comparison of colors illuminated (by the luminescent light) to those same colors illuminated, for example, by direct `white` noon sunlight. (Direct `white` sunlight typically between noon and 2:00 P.M. is the practical standard for determining color for human vision.) Manufacturers of luminescent light tubes try to blend phosphors to produce different bandwidth distributions of radiant energy usually identified with a proprietary trademark, e.g., LUMILUX.RTM.. Descriptive terms such as cool white, warm white, daylight are also frequently relied upon. However, most luminescent light tube manufacturers ultimately resort to characterizing the distribution of different bandwidths of light emitted by their blends of phosphors as producing an effect of illumination equivalent to that produced by incandescent Tungsten filaments at particular temperatures expressed in degrees Kelvin (.degree.K), in tacit recognition of the predominance of Stefan-Boltzman blackbody emission standards.
A better index for characterizing the light output of luminescent light tubes having a selected blend of phosphors emitting a distribution of different narrow spectral bandwidths of light would be the SRGB.RTM. standard developed by the Applicant which characterizes the relative radiance of respective red, blue and green primary color bandwidths of sustained luminescent light emanated by a blend of phosphors reflecting from known sets of standard gray scale charts and color band charts.
In particular, the color of a surface is the bandwidths of light reflected from that surface. Such reflected light can be captured, digitally imaged and then sampled using conventional eye dropper tools associated with most computer graphics, design, and image processing software programs. The software eye dropper tools measure and/or characterize such parameters as brilliance, saturation, hue, tint, shade or whatever, in terms of the various color-model systems used by the particular program for specifying color. In a sense, the optical capture system, and associated computer and software tools function as a reflection meter. Diffusely reflected light from a standard chart can be sampled to provide a quantitative color evaluation of its spectral in terms of color(s) reproduced and observed by a human being directing the optical capture system and controlling the computer system.
For example, in the RGB additive model, typical CRT television or computer monitor screens reproduce the color yellow, not spectrally present, by combining various brightness values of red, green, and blue light. James Clerk Maxwell initially demonstrated this effect to the Royal Institute in London in 1861. The L*a*b* (Lab) model developed by CIE.sup.1 mathematically specifies a luminance or lightness (L) value and two chromatic components values (a) specifying a range from green to magenta, and (b) specifying a range from blue to yellow in a way that is supposed to be device independent. The CMY and CMYK color-model system for photography and printing are subtractive/multplicative models that specify values for cyan (C), magenta (M), yellow (Y) filters and ink which absorb light. Values for black (K) inks are specified in printing because available C, M & Y inks combine to reflect a muddy brown. [See Van Nostrand's Scientific Encyclopedia 7th Edition, Vol. 1, pp. 36 & 701, Vol. 2 pp. 2203, 2714] In HSB and HLS color models, an achromatic `gray scale` value termed `brilliance` (B) or `lightness` (L) is specified along with two chromatic values specifying `hue` (H) and `saturation` (S). Saturation is a parameter relating to purity of the color, gray being zero. In the HSB model, colors having a more pronounced hue are more chromatic, i.e., differ more from a gray of the same `brilliance` or `lightness` `Brilliance` and `hue` can in turn be related by using such terms as `tints` and `shades.` A chromatic color having little `hue` but high `brilliance` is termed a `tint`, e.g., pink, whereas color of low `hue` and low `brilliance` is termed a `shade`, e.g. brown.
 FNT .sup.1 Centre Internationale d'Eclairage, an international organization which began establishing specifications for color in 1931. CIE has developed a number of comparable standards including CIE XYZ, CIE xyY, CIE L*u*v* and CIE L*a*b*. The television broadcast industry in fact specifies desired chromaticities in picture tube output which then relate to gamma corrected voltages corresponding to red green and blue signals. See 47 CFR .sctn. 73.682(20) (iv).
Modern personal computers and associated graphics, design and imaging software programs and tools provide RGB image displays which allow users to manipulate and evaluate color by varying values in one or more of the common and proprietary color modeling schemes using side-by-side color comparison boxes. Such computers and software tools thus, in a very real sense, allow the bandwidth sensitivity of human perception to be integrated into the evolution of illumination standards for producing images of studio subjects and talent.
Titanium dioxide also in the emulsion coatings of luminescent light tubes scatters and mixes the light emissions from the different phosphor compounds in the coating. Ad Lagendijk of the University of Amsterdam and the FOM-Institute for Atomic and Molecular Physics in the Netherlands at the American Physical Society Meeting in March 1991 held in Cincinnati, Ohio, reported a discovery that the velocity of light propagating through a highly disordered scattering medium such as a dispersion of titanium dioxide, appears to be one tenth of that previously assumed. [See Science News Mar. 23, 1991, Vol. 139, No. 12, p. 182.] Nabil M. Lawandry of Brown University reported in the March 1994 issue of Nature, reported that he and his co-workers discovered that certain dyes when dissolved in a liquid containing tiny particles of titanium dioxide when stimulated by an external energy source, amplify the (luminescent) light emitted by the excited dye (phosphor) molecules. In their experiment, Lawandry et al used a green laser to excite photoluminescent molecules of rhodamine dissolved in menthol. Adding titanium dioxide particles greatly amplified the emitted light. The surprising result was that a medium containing particles that reflect light in all directions can amplify emitted radiation. [See also Science News Apr. 9, 1994, Vol. 145, No. 15, pp. 228-229.]
The stability of light emission from luminescent light tubes and capability of blending phosphors to produce distributions of different spectral bandwidths of luminescent light emission permits tailoring to achieve a proper balance of sustained red blue and green bandwidth light emissions optimized for electron scanning/television/video cameras, color films and even two human eyes. However, electronic scanning cameras, including charge-coupled devices (CCDs) which record television and video color images do not mimic human eyes, but rather generate signals representative of spectral energy in separate red, blue and green light bandwidths reflecting off an object. This is accomplished by separating red, green and blue images of the object from the incoming light using, for example, a spilt-cube separation optical system that has appropriate Diachronic coatings which allow transmission of one bandwidth along the principal optical axis while reflecting the other two bandwidths into two adjacent channels typically located on opposite sides of the principal optical axis. The three separate color images are directed onto and converted into electrical image signals by three separate photosensitive or CCD surfaces. Single tube systems use a subtractive color process interposing an array of crossing filters strips to selectively pass representative bandwidths of light. In either case, the resultant electrical signal is then processed to produce signals representative of the respective red, blue and green light bandwidths reflected from the object. [See Television and Audio Handbook (1990) K. Blair Benson & Jerry C. Whittaker pp. 6.6, 6.7; and Television Engineering Handbook (1986) K. Blair Benson Chap. 4, pp. 4.56-4.76, & Chaps. 11.
The electrical images signals obtained by such electron scanning cameras can then be manipulated to provide color corrected or false color images when reproduced at a television/video monitor screen. It is even possible with present day CHROMAKEY videos systems to electronically subtract the image signal in one or more channels and substitute an image signal from a completely different source to produce a composite image at the monitor screen. The electronic systems driving the monitor screens or displays utilize the electrical images signals generated by the cameras for driving an additive color process for reproducing hues of the object imaged. [See Television Engineering Handbook (1986) K. Blair Benson Chap 12]
In contrast to electronic imaging, in film, color images are reproduced principally by a subtractive color process using colorant filters for controlling the amounts of reflected red blue and green light from an object to create a positive or negative image of the object in a light sensitive chemical emulsion. [See Van Nostrand's Scientific Encyclopedia 7th Edition, Vol. 2 pp. 2203, 2714]
Finally, the UV radiation flashes driving luminescent light emissions from phosphors impart cyclic variation to the stimulated light. If the cyclic variation is slow as when using a 60 Hertz ballast (producing 120 flashes per second), rapidly moving objects illuminated produce "blurred ghost like" images referred to as a stroboscopic effect. The illumination industry characterizes cyclic variation in luminescent light emissions as flicker specifying a Flicker Index which is a relative measure of the cyclic variation in output of various sources at a given power frequency.
Catadioptric lenses use both reflection and refraction to redirect or bend light and can be utilized disperse, collect, collimate and gather or concentrate light in a manner similar to Fresnel lenses. [See U.S. Pat. No. 4,755,921, Nelson, & U.S. Pat. No. 4,791,540. Dreyer et al.] However, as explained in U.S. Pat. No. 5,568,324, Nelson et al, because the index of refraction is frequency/wavelength dependant in optically transmissive materials, catadioptric lens systems like other refractive optical components, exhibit chromatic aberration, i.e., optical materials refract different wavelengths of light dispersively. In U.S. Pat. No. 5,568,324, Nelson et al presents a solution a problem of chromatic aberration in an over head projection (OHP) system using a light source located below and to one side of a planer face of a divergent catadioptric lens by utilizing a doublet condensing lens system where the divergent catadioptric lens has a planer face and a structured face of prismatic ridges in combination with a convergent catadioptric lens also having a planer face and a structured face of prismatic ridges where the respective structured faces of the respective catadioptric lenses are located in an aligned facing relationship.